This is a proposal to continue our study of the fine structure and synaptology of central nervous system centers by means of the Golgi technique and electron microscopy. The Golgi technique is capable not only for revealing the details of nerve cells but also the details of nerve fibers. Used in combination, thick Golgi sections and ultra-thin electron microscopic sections complement each other; the former provide the necessary optical microscopic data for interpreting the latter. At present we are investigating the neural centers in the basal ganglia, i.e. the caudate nucleus, the putamen and the globus pallidus and centers connected to the basal ganglia, i.e. the substantia nigra, the subthalamic nucleus, the nucleus centre median, the nucleus parafascicularis, the ventralis anterior-ventralis lateralis of the thalamus. These nuclei are being studied in Golgi preparations of the adult monkey, Macaca mulatta (preparations available in our collection) and in normal and experimental electron microscopic material of the squirrel monkey, Saimiri sciureus.